The products of metabolism of unsaturated fatty acids by oxygenases (prostaglandins, leukotrienes, and HETEs, Hydroxyeicosatetraenoic acids) are well established as important signaling molecules and mediators. Based on these precedents, the occurrence of a peculiar hydroxy fatty acid metabolite, 12R- HETE, in human epidermis, and particularly its prominence in proliferative skin diseases exemplified by psoriasis, is strongly suggestive of its significance to the pathophysiology of skin. Although 12R-HETE was usually considered a product of cytochrome P450, recently we established that a lipoxygenase is the enzyme type responsible for 12R-HETE synthesis in psoriasis. From human keratinocytes we have also cloned and expressed a 12R- lipoxygenase that can account for 12R-HETE overproduction in proliferative skin disease. In this project we will examine the role of this newly discovered enzyme by: 1. Characterization of the human 12R-lipoxygenase and its catalytic activities. 2. Establishing the tissue and cellular localization of the enzyme, including in psoriasis and other proliferative and inflammatory skin disease. 3. We will assess 12R-Lox expression in established mouse models of skin disease, and 4. Develop and characterize transgenic animals overexpressing the human 12R-lipoxygenase with targeted expression to epidermis. These studies will elucidate the sites and regulation of 12R-HETE synthesis, assess its biosynthesis in normal and diseased tissues, elucidate the effects of 12R-HETE overexpression in animal models, and will prepare the way for a rational appraisal of lipoxygenase inhibitors as a potential therapy in proliferative skin disease.